Moral insanity referred to a type of mental disorder consisting of abnormal emotions and behaviours in the apparent absence of intellectual impairments, delusions, or hallucinations. It was an accepted diagnosis in Europe and America through the second half of the 19th century.
The physician James Cowles Prichard first used the phrase to describe a mental disorder in 1835 in his Treatise on insanity and other disorders affecting the mind. He defined moral insanity as: “madness consisting in a morbid perversion of the natural feelings, affections, inclinations, temper, habits, moral dispositions, and natural impulses, without any remarkable disorder or defect of the interest or knowing and reasoning faculties, and particularly without any insane illusion or hallucinations.”
The concept of moral insanity was indebted to the work of physician Philippe Pinel, which was acknowledged by Prichard. Pinel had described mental diseases of only partial, affective, insanity. His concept Manie sans délire (Latin – mania sine delirio; French – folie raisonnante or folie lucide raisonnante, monomanie affective; German – Moralisches Irresein) referred to insanity without delusion. That is, the sufferer was thought to be mad in one area only and thus the personality of the individual might be distorted but his or her intellectual faculties were unimpaired.
The term ‘moral’, at that time and taken originally from French, could mean emotional rather than necessarily referring to ethics.